It seems these are the two most common levels people using for mining. For the sake of argument, let's ignore the issue of lava for now. What do the charts say about finding diamonds if my feet are at 11 as opposed to 12? Assuming one mines by digging a 1x2 tunnel, you are exposing the surfaces of 4 levels of blocks. In the case of standing at Y = 11, you are exposing block surfaces from levels 10, 11, 12 and 13. When mining at Y = 12, you are exposing block surfaces from levels 11, 12, 13 and 14. Do the charts really indicate a *significant* difference in diamond concentrations between those levels? I'm guessing they don't. So it's really about the lava then, right? On that note, I mine at 11, my thinking being if I fall in lava from Y = 12 there's a chance I can't get out, whereas with falling in from Y = 11, I know I can get out.